602 ORGANS OF SECRETION. 



the mesenteric artery, along with the spleen. The veins 

 (o. p.) returning from the alimentary canal, the spleen, and 

 the pancreas, unite below the liver to form the vena portarum 

 (h.) which ramifies through the right (m.) and left (n.) lobes 

 of that organ. 



As the alimentary canal passes straight through the body 

 in the embryos of vertebrata, the great chylopoietic glands, 

 the liver and the pancreas, are developed from its anterior 

 part, on the median plain, like the lungs from the oesophagus. 

 In the embryo of the lizard, the liver appears at first as a 

 short, hollow, bifid follicle continued from the intestine, and 

 numerous tubuli bud out from the whole surface of its thick 

 vascular parietes, which extend, ramify, and compose the 

 entire lobules and lobes. The thymus gland, which first 

 makes its appearance in the reptiles, is there a permanent 

 organ, as it is also in some of the lower mammalia, as the 

 cetacea and the rodentia. Some predaceous saurians, as 

 the aligators, possess distinct anal glands, like many carni- 

 vorous quadrupeds, which secrete a strongly odorous subs- 

 tance, having the odour of musk, and the same structure 

 appears to belong to some chelonian reptiles, and to the 

 rattle-snakes and many other serpents, both noxious and 

 innoxious. Besides these anal musk-glands, most of the 

 crocodilian reptiles present two simple follicular glands under 

 the lower jaw, which pour out on the surface of the skin a 

 thick fluid with a similar musky odour. In some lizards, 

 these odorous glands open by distinct external apertures on 

 each side of the anus, and in most of the saurian reptiles 

 there are numerous external inguinal pores for the discharge 

 of a similar strongly odorous secretion at the breeding season. 

 The cutaneous follicles of the Indian gecko secrete a fluid 

 which is said to have the same acrid and poisonous pro- 

 perties as that of the toad. The glandula lachrymalis and 

 , Harderi are already distinct in the orbit of reptiles, and even 

 in serpents where the skin passes transparent and conti- 

 nuous over the front of the eye-ball ; and the urinary and 

 genital glands have here attained a high development. 



The liver is already perceptible in the embryo of birds, as of 

 the fowl, on the third day of incubation, and appears as a 

 simple bifid hollow projection from the anterior median aspect 

 of the straight alimentary canal. These two follicles or primi- 

 tive lobes extend, enlarge, draw out the digestive tube to in- 



